Ink jet technology continues to be improved in order to increase printing speed and print quality or resolution. One means for improving print speed and quality is to increase the number of nozzle holes in an ink jet print head and to decrease the diameter of the nozzle holes. However, improvements in print speed and quality often result in operational problems not experienced with lower quality slower speed printers.
In an ink jet printer, ink is provided to the print head from an ink cartridge or supply tank. The ink flows from the tank through a connecting conduit from the ink cartridge through an ink via in a semiconductor chip or around the edges of a semiconductor chip and into ink flow channels and an ink chamber. Each ink chamber is situated in axial alignment with a corresponding nozzle hole and a heater resistor defined on the surface of the semiconductor chip. Electrical impulse energy applied to an ink ejector adjacent an ink chamber causes ink adjacent the ejector in the chamber to be forced through a nozzle hole onto a print medium. By selective activation of a plurality of ink ejectors on a print head, a pattern of ink dots are applied to the print medium to form an image.
Conventional ink jet print heads desire improvement, particularly with regard to the manufacture of heater chips for use with print heads. Particularly desired improvements in the manufacture of heater chips include improvements in the planarity of such chips and in the uniformity of the planarizing layer thickness. Defects in conventional chips result in print heads that are prone to misdirected ink drop ejection, poor nozzle plate adhesion, and reduced corrosion resistance.
Ink jet print heads typically include a print head body containing a semiconductor substrate and a nozzle plate attached to the substrate. The substrate/nozzle plate assembly is received by a chip pocket in the print head body. Ink is supplied to the substrate/nozzle assembly from an ink reservoir in the print head body generally opposite the chip pocket. The semiconductor substrate for a thermal print head is typically a silicon substrate containing a plurality of ink ejection devices such heater resistors formed on a device side thereof. These substrates are referred to as “heater chips.”
FIG. 1 shows a portion of a prior art heater chip 10 having a plurality of heater resistors 12 formed on a device side 14 thereof. A nozzle plate 16 (FIG. 3) having ink ejection nozzle holes 18 corresponding to the heater resistor sites is generally attached to the chip 10. The device side 14 of the chip 10 also includes conductors 17 from one side of the heater resistors 12 to driver circuitry 19 for supplying electrical impulses from a printer controller to activate the heater resistors 12 for printing. A conductor 21 is connected from the opposite side of the heater resistors 12 to a common power conductor 23. Upon activation of the heater resistors 12, ink supplied through an ink via 20 in the chip 10 is caused to be ejected toward a print media through the nozzle holes 18 (FIG. 3). The chip 10 is configured for use with a top-shooter type print head, wherein the ink is ejected from the nozzle plate 16 attached to the device side 14 of the chip 10.
With reference to FIGS. 2A–2B and 3, the chip 10 contains various layers such as a first conductive metal layer 22, a passivation layer 24, and a cavitation protection layer 26 deposited on the device side 14 thereof. The resistors 12 and 33 are defined by a resistive layer 25 and each heater resistor 12 and 33 corresponds to one of the nozzle holes 18 in the nozzle plate 16 for heating and ejecting ink toward a print media. As will be noted, there is a significant topographical variation 27 adjacent end 28 of the heater array.
FIG. 3 shows the nozzle plate 16, not to scale, attached to the heater chip 10. The topographical variation 27 complicates attachment of the nozzle plate 16 and results in a deformation in the orientation and shape of the nozzle hole 18, particularly near orifice 30 of the nozzle hole 18. Deformation of the shape of the nozzle hole 18 results in an ink ejection path, represented by the arrow 32, which deviates from the desired ink ejection path, represented by arrow 34. The angle of the desired but previously unachievable path 34 relative to the resistor is preferably about 90 degrees. The angle represented by the intersection of arrows 32 and 34 in FIG. 3 is exaggerated to illustrate deviation from an ideal ejection path. The angle of the path 32 typically achieved generally ranges from about 90 to about 90.6 degrees. Although a 0.6° deviation from ideal may appear to be minor, the resulting droplet misplacement is significant given the distance the droplet travels before impacting the recording medium and the high placement precision required for quality printing.
As will further be noted, the heater resistor 33 at the end 28 of a heater array 35 tends to have a relatively higher current path resistance, and hence different energy, than the interior heater resistors 12. This higher resistance results from the availability of only a single current path through the heater resistor 12 adjacent the end 28 of the heater array 35, as represented by arrows 36.
Accordingly, there is a continuing need for improved ink jet printheads as printing speed and print resolution continue to increase. There is also a need for improved methods for making high resolution ink jet printheads.